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Semiconductor devices are formed from a flat, thin wafer of a semiconductor material, such as silicon. The wafer must be polished to achieve a sufficiently flat surface with no or minimal defects. A variety of chemical, electrochemical, and chemical mechanical polishing techniques are employed to polish the wafers.
In chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d), a polishing pad made of a urethane material is used in conjunction with a slurry to polish the wafers. The slurry comprises abrasive particles, such as aluminum oxide, cerium oxide, or silica particles, dispersed in an aqueous medium. The abrasive particles generally range in size from 100 to 200 nm. Other agents, such as surface acting agents, oxidizing agents, or pH regulators, are typically present in the slurry.
The urethane pad is textured, such as with channels or perforations, to aid in the distribution of the slurry across the pad and wafer and removal of the slurry and grindings therefrom. In one type of polishing pad, hollow, spherical microelements are distributed throughout the urethane material. As the surface of the pad is worn away through use, the microelements provide a continually renewable surface texture.
The present invention relates to a polishing pad for polishing a substrate in the presence of a slurry comprising abrasive particles and a dispersive agent. The polishing pad uses a component, preferably fibrous, within a polymer matrix component. The fibrous component is soluble in the slurry, such that fibers present at the polishing surface of the pad dissolve upon contact with the slurry to provide a void structure on the polishing surface. The void structure provides pores that enhance the polishing rate and uniformity by increasing the mobility of the abrasive particles in the slurry while reducing scratching of the polished surface. The pores act as temporary storage areas for the abrasive particles, thus reducing highly frictional contact between the abrasive particles and the polished surface.
More particularly, the polishing pad comprises a first layer having a polishing surface and a backing surface. The first layer is formed of the fibrous component in the polymer matrix component. The fibrous component comprises fibers soluble in the slurry sufficiently to provide a void structure in the polishing surface. The solvent may be either the dispersive phase of the abrasive particles or another material added to the slurry during polishing. The polishing pad also comprises a backing structure comprising an adhesive layer or layers fixed to the backing surface of the first layer, so that the polishing pad may be affixed to a tool.
The nature of the void structure on the polishing surface of the polishing pad is determined by parameters such as the rate of dissolution of the fibers in the solvent, the ratio of fibers to matrix, the shape and size of the fibers, the orientation of the fibers, the density of the fibers both in area and volume, and the presence and amount of any insoluble fibers. Suitable fibers for semiconductor wafer polishing, which are soluble in an aqueous slurry, include polyvinyl alcohol and maleic acid and their derivatives or copolymers.
Additives that further enhance polishing and/or assist in the removal of residues generated during polishing may be incorporated in the fibrous component or be applied as a topographic coating to the fibrous component. These additives are released at a controlled rate during polishing.
The polishing pad applies to a diversity of applications including semiconductor wafer polishing known as chemical mechanical polishing (CMP) and other polishing applications for metal, ceramic, glass, wafers, hard disks etc., that use a liquid medium to carry and disperse the abrasive particles.